This invention relates to conversion of fluid flow to electricity generally, and particularly to piezoelectric transducer devices for converting wind flow to AC (alternating current) power and for determining wind velocity.
Piezoelectric materials have been used to generate electrical power from wind action. One such system is described, for example, in U.S. Pat. No. 4,536,674 entitled Piezoelectric Wind Generator, issued Aug. 20, 1985 to V. Hugo Schmidt. Another such system is described in U.S. Pat. No. 3,239,678 entitled Piezoelectric Power System, issued Mar. 8, 1966 to C. Kolm et al. In many such prior systems, fluid flow pressures (e.g., pressures applied to piezoelectric materials by wind flow, or by flow of exhaust gases) had to be substantial in order to provide adequate power generation. Such systems generally were not able to generate power at lesser fluid pressures.
Also, some prior systems generate AC power by rotational action, employing windmill or turbine-like blades for driving wire loops and cutting magnetic field lines. Such systems are generally bulky, however, and entail substantial wear and tear because of their rotational motion.
Further, many such power generation systems do not provide related information such as fluid flow velocity. Many such prior systems (e.g., pressure-actuated systems or devices such as the Pitot tube) measure fluid velocity by applying the Bernoulli principle, i.e., EQU P+1/2.rho.V.sup.2 =constant
where P represents the pressure exerted by the fluid, .rho. represents the fluid's density, and v represents the velocity of the fluid. A change in density is represented as: ##EQU1## and a change in velocity is represented as: ##EQU2## However, such prior systems often do not distinguish between pressure changes that are due to density changes and pressure changes that are due to velocity changes. When such devices experience a pressure change (.delta.P), they sometimes erroneously interpret the pressure change as due to a velocity change (.delta.v) when, in fact, the pressure change may be due to a change in density (.delta..rho.). Such prior systems are unreliable and error prone. For example, given a fluid velocity v=500 miles per hour and the value ##EQU3## such Bernocilli type velocimeter devices would produce a velocity error ##EQU4## or -12.5 miles per hour.
What is needed and would be useful, therefore, is a more efficient power generation system which could operate without substantial rotational wear and tear, and which could provide accurate wind velocity measurements.